A device as mentioned is known from US 2003/196294. In the case described in this document, the device is an appliance for cleaning a surface, the functional body is a brush for removing dirt from the surface, and the safety means comprise a magnetic clutch which is arranged in a power transmission coupling between the brush and a motor for driving the brush.
According to the teaching of US 2003/196294, it may occasionally happen that when the cleaning appliance is used, and the brush is made to perform a rotating movement, the brush becomes entangled with foreign objects, which cause the brush to slow down or stop altogether. In such cases, the foreign object may be damaged by the strain applied to the object by the rotating brush when the brush becomes jammed. Alternately, or in addition, the motor for driving the brush may become damaged. For example, in case the motor is an electric motor, the motor could overheat by drawing an excessive current due to the brush jam condition.
By using a magnetic clutch, it is possible to stop the brush rotating if the brush becomes jammed. This type of clutch comprises two elements such as opposed plates which are provided with magnets. Under normal conditions, attractive forces between the magnets on the opposed plates will magnetically couple the plates together. Accordingly, the rotation of one plate will cause the other plate to rotate. However, as the plates are not physically connected, if a predetermined amount of torque is applied to one of the plates, which happens when the brush becomes jammed, the plates will become magnetically decoupled.
Consequently, continued rotation of one of the plates will not cause the opposed plate to rotate, whereby damage to the brush, any object entangled in the brush, as well as the motor for driving the brush is prevented.
A practical example of a foreign object which may cause the brush to jam is an electric cord lying on the surface to be cleaned. When this happens, an extremely dangerous situation may occur when the brush is not decoupled from the motor. The fact is that the brush and the cord can interact in such a way that the cord is stripped from its insulating layer, leaving the bear copper of the cord either to cause a short circuit, and thereby a possible fire, or to shock the user when trying to get the cord out by hand.
It appears in practice that the use of a clutch for decoupling the brush from the motor does not guarantee that damage to an electric cord does not occur. Especially when a relatively thick electric cord is encountered by the brush, it may happen that the cord does not wrap around the brush due to its inflexibility, so that the brush rubs over the cord, while the friction is not enough for reaching the level of torque at which the clutch decouples. In view of the possibility of such a situation, it is an object of the present invention to improve the safety mechanism of a device comprising at least one movably arranged functional body which is used in performing an action on a surface, such as a brush which is used in performing a cleaning action as described in the foregoing.